Membrane module for fluid filtration

ABSTRACT

Embodiments of the invention provide a membrane module including a first plurality of fibers capable of filtering fluids that are helically wound in layers creating a mono helix. Fluids to be treated can flow radially with respect to a longitudinal axis of the mono helix or parallel to the longitudinal axis of the mono helix. The membrane module can further include a second plurality of fibers that are helically wound with the first plurality of fibers to create a dual helix. The second plurality of fibers can have different properties than the first plurality of fibers in order to achieve different filtering functionalities.

BACKGROUND

Membrane bioreactors (MBRs) are widely used for wastewater treatmentbecause of their improved performance resulting in better water qualityand minimal space requirements compared to conventional treatmentprocesses. MBRs include immersed porous membranes to extract clean water(i.e., permeate water) from waste that is mixed with a biomass includingactive aerobic organisms. This mixture of waste and biomass is generallycalled a mixed liquor. The immersed membranes generally include tubularhollow fiber membranes or plate-type filtration membranes. Permeatewater is removed from the mixed liquor by passing through the pores ofthe membranes.

Membrane fouling remains a significant challenge for conventional MBRs.This is due to the accumulation of soluble and particulate materialsfrom the mixed liquor onto and into the porous membranes. Fouling of theporous membranes leads to increased energy costs, poor operatingconditions, poor efficiency, and frequent membrane replacement.Conventional treatments for cleaning the porous membranes includeaeration, intermittent permeation, permeate backwashing, airbackwashing, and chemical cleaning. Aeration generally involves streamsof large, coarse air bubbles being provided at the base of the membranesin order to scour the fibers as they float upward toward the top of themembranes. Aeration (both coarse and fine bubble aeration) is also usedto circulate the mixed liquor to help re-suspend solids. Due to the airbubbles only being released at the base of the membranes, dead zonesdeprived of sufficient cleaning or circulation are often present inconventional MBRs. The other conventional treatments for cleaning theporous membranes require periodically stopping filtration, whichincreases energy costs and decreases permeate flow.

Some conventional MBRs use moveable fibers to help mitigate the foulingproblem. The moveable fibers are fixed only at one end so that they cansway and rub against each other to help reduce fouling. However,breakage is a problem with these moveable fibers due to highermechanical stress at their fixed ends, as well as abrasion due torubbing against each other. As a result, these moveable fibers must bereinforced, which increases membrane costs.

SUMMARY

Some embodiments of the invention provide a membrane module including aplurality of fibers that are helically wound in layers. The plurality offibers can be capable of filtering fluids. The plurality of fibers cancreate a mono helix through which fluids flow radially with respect to alongitudinal axis of the mono helix or parallel to the longitudinal axisof the mono helix.

Some embodiments of the invention provide a membrane module including afirst plurality of fibers and a second plurality of fibers. The firstplurality of fibers can be capable of filtering fluids. The secondplurality of fibers can be helically wound along at least a portion of alength of the first plurality of fibers in order to create a dual helix.The second plurality of fibers can have different properties than thefirst plurality of fibers in order to achieve different filteringfunctionalities.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a wastewater treatment process includingconventional non-MBR and MBR methods.

FIG. 2 is a perspective view of a mono-helix fiber membrane according toone embodiment of the invention.

FIG. 3 is a schematic illustration of the mono-helix fiber membrane ofFIG. 2 surrounded by a mixed liquor according to some embodiments of theinvention.

FIG. 4 is a perspective view of a membrane module including themono-helix fiber membrane of FIG. 2 according to some embodiments of theinvention.

FIG. 5A is a schematic illustration of the mono-helix fiber membrane ofFIG. 2 surrounded by a mixed liquor.

FIG. 5B is a close-up illustration of the mono-helix fiber membrane ofFIG. 5A.

FIG. 6 is a perspective view of a dual-helix fiber membrane according toanother embodiment of the invention.

FIG. 7A is a schematic illustration of the dual-helix fiber membrane ofFIG. 6 surrounded by a mixed liquor.

FIG. 7B is a close-up illustration of the dual-helix fiber membrane inFIG. 7A.

FIG. 8 is a cross-sectional view of a mono-helix or dual-helix membranemodule through which fluid flows radially.

FIG. 9 is a cross-sectional view of a mono-helix or dual-helix membranemodule through which fluid flows parallel to the membrane and core.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

The following discussion is presented to enable a person skilled in theart to make and use embodiments of the invention. Various modificationsto the illustrated embodiments will be readily apparent to those skilledin the art, and the generic principles herein can be applied to otherembodiments and applications without departing from embodiments of theinvention. Thus, embodiments of the invention are not intended to belimited to embodiments shown, but are to be accorded the widest scopeconsistent with the principles and features disclosed herein. Thefollowing detailed description is to be read with reference to thefigures, in which like elements in different figures have like referencenumerals. The figures, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope ofembodiments of the invention. Skilled artisans will recognize theexamples provided herein have many useful alternatives and fall withinthe scope of embodiments of the invention.

Some embodiments of the invention provide a membrane module including aplurality of fibers that are helically wound in layers to create a monohelix. Other embodiments of the invention provide a membrane moduleincluding a first plurality of fibers and a second plurality of fibersthat are helically wound to create a dual helix. The mono and dual helixmembrane modules are capable of filtering fluids for purposes of variousfluid filtration applications. For example, embodiments of the inventioncan be used in several general categories of applications, includingdrinking water purification, wastewater treatment, and industrialprocess water treatment. More specifically, embodiments of the inventioncan be used in various fluid treatment systems, including but notlimited to, the following: MBR wastewater treatment systems,ultrafiltration chemical reactor systems, ultrafiltration membranesystems, dairy dewatering systems, protein fractionation systems, oiland water separation systems, gas addition systems, etc. Althoughembodiments of the invention can be used in each of these types of fluidfiltration systems, the invention is generally described herein as beingused in a MBR wastewater treatment process.

FIG. 1 illustrates non-MBR and MBR wastewater treatment processes 10.The water treatment processes 10 can be used in municipal, industrial,commercial, or residential wastewater treatment for various applicationsincluding, but not limited to, food and beverage production, chemicaland pharmaceutical manufacturing, irrigation, landfill leachate, metalfinishing and steel production, and pulp and paper processing. The firststep includes collecting the water to be treated or the raw sewage (step12). The raw sewage is then filtered through a screen to remove grit andlarger objects (step 14). The process steps in box 16 (steps 18-38)represent steps during a non-MBR water treatment process. In the non-MBRprocess, the filtrate from the screening grit removal (step 14) goesthrough a primary clarifier to remove solids (step 18), and then into anaeration basin where the activated sludge removes or converts solublecontaminants (step 20). The activated sludge then goes through asecondary clarifier (step 22), a live softening process (step 24),another clarification process (step 26), air stripping (step 28),recarbonation (step 30), sand filtration (step 32), and gas absorption(step 34). Sludge removed during the primary and secondary clarifier(steps 18 and 22) is drained into a sludge digester to be broken down(step 36). Sludge from the sludge digester (step 36) and sludge removedduring the other clarification process (step 26) is sent to the sludgedewatering disposal (step 38). The resulting filtrate from the gasabsorption step (step 34) is the final treated water, ready to bedischarged (step 40). Sludge can also be recirculated from theclarification process (step 26) to the secondary clarifier (step 22).

For a MBR water treatment process, the steps in box 16 (steps 18-38) canbe replaced by the steps in box 42 (steps 44-48). The filtrate from thescreening grit removal (step 14) is processed in a membrane bioreactor50 (step 44) to separate water from sludge and remove solublesubstances. Dewatered sludge (from step 44) can be removed by a sludgedewatering disposal (step 46). Permeate water from the membranebioreactor 50 (from step 44) can be further filtered by ultrafiltration(step 48). Step 48 can be replaced by other filtration processes, suchas microfiltration or nanofiltration, depending on the application. Theresulting filtrate or permeate water from ultrafiltration (step 48) isthe final treated water, ready to be discharged (step 40). As shown inFIG. 1, the use of the membrane bioreactor 50 can significantly simplifythe water treatment process 10. In some embodiments of the invention,the components of the membrane bioreactor 50 (step 44) and thecomponents of the ultrafiltration process (step 48) can be positioned inthe same or separate tanks, chambers, or pressurized vessels.

FIG. 2 illustrates a mono-helix fiber membrane 52 according to oneembodiment of the invention for use in the membrane bioreactor 50, forexample. The mono-helix fiber membrane 52 can include a core 54 andfibers 56 helically wound around the core 54. Although the core 54 isshown as a cylinder with a circular cross-section in FIG. 2, someembodiments can include a core having other cross-sections, such assquare, elliptical, triangular, etc. The core 54 can be a solid cylinderor a porous, hollow cylinder. In some embodiments, the inside of thecore 54 can include a packed bed of filtration media. In someembodiments, the core 54 can be perforated at one or more portions alongits length. An ultraviolet light source inside or outside the core 54can be included, in some embodiments, for sterilization purposes. Inother embodiments, the mono-helix fiber membrane 52 does not include acore 54, but rather the fibers 56 are helically wound into a similarcylindrical shape, with a supporting structure at either end.

In some embodiments, the fibers 56 can be permeable, hollowultrafiltration membranes and can be coupled or potted (along with thecore 54 or the supporting structures) at one or both ends to a header ortubesheet 58. The header 58 can be coupled to a permeate manifold inorder to collect and direct permeate water. In other embodiments, thefibers 56 can be microfiltration or nanofiltration fibers.

The fibers 56 can be wound helically around the core 54 at a consistentor variable wind angle. The wind angle, defined with respect to the core54 in a horizontal position, can be the angle at which the fiber 56 islaid across the core 54 with respect to the vertical axis. For example,fibers 56 wound at a 90-degree wind angle would be parallel to thehorizontally-positioned core 54. The fibers 56 can be wound around thecore 54 in layers, where a layer is defined as a fiber 56 wound from oneend to the other end and the return of the fiber 56 to the first endconstitutes another separate layer. In some embodiments, the fibers 56can be wound as disclosed in United States Patent ApplicationPublication No. 2008/0072754 in the names of Burban et al., the entirecontents of which is herein incorporated by reference.

The layers of fibers 56 can be asymmetrically wound about the core 54 tocreate a mono helix 60. The density of the layers can change withrespect to either a radial distance from a center of the core 54 or anaxial distance from an end of the core 54. For example, the mono helix60 can be more dense in an interior portion (i.e., closer to the centerof the core 54) and become less dense in an exterior portion (i.e.,further from the center of the core 54). In addition, the fibers 56 canvary in texture, cross-sectional shapes, surface structure, and/ordimensions (such as lumen size), in some embodiments.

The fibers 56 can be constructed of a polymeric, hydrophilic materialwith a lumen 62, as shown in FIG. 3. For example, the fibers 56 can beconstructed of polysulfone, polyvinylidene fluoride, polyvinyl chloride,polyethylene, polypropylene, etc. The pressure inside of the lumens 62can be lower than the pressure outside the fibers 56, creating a vacuumin the lumens 62. For example, a vacuum can be applied to the lumen 62or the environment outside the fibers 56 and can be held at a pressureabove atmospheric pressure. Due to the pressure difference, permeatewater 64 from a surrounding mixed liquor 66 can be drawn through poresof the fibers 56 into the lumen 62 for an outside-in filtrationconfiguration. In other embodiments, the fibers 56 can be used in aninside-out filtration configuration, where the mixed liquor 66 iscirculated through the lumen 62 at a higher pressure and permeate water64 is drawn outside of the fibers 56 through the pores to alower-pressure environment. The pores of the fibers 56 can be consistentor variable in size and can be between about 0.01 microns and about 0.2microns in diameter. The pores can also vary outside this range,depending on the application. In addition, the mono helix 60 can haveconsistent or varying patterned porosities along its axial length.

In some embodiments, the mono-helix fiber membrane 52 can include one ormore mono helixes 60 coupled together to the header 58 that is submersedin a membrane bioreactor tank. In other embodiments, as shown in FIG. 4,the mono-helix fiber membrane 52 can include one or more mono helixes 60in a cylindrical housing or cartridge 68 with end caps 70. The monohelix or helixes 60 can be fixed at both ends to headers 58 so that thefibers 56 are substantially stationary or can be fixed at only one endto a single header 58 so that the fibers 56 are moveable (i.e., cansway).

In the stationary configuration, the use of the core 54 and the designof the mono helix 60 supports the fibers 56 and prevents them frombreaking. Also, in the stationary configuration, the reinforcement ofthe core 54 and the mono helix 60 can allow reduced fiber maintenance,as well as the use of finer and cheaper fibers 56, reducing the cost ofthe mono-helix fiber membrane 52. In the dynamic configuration, theswaying motion can help reduce fouling on the fibers 56. In addition,the mechanical strength of the mono helix 60 reinforces the fibers 56and prevents fiber breakage due to increased mechanical stresses fromthe swaying.

FIG. 5A is a schematic illustration of a portion of the MBR 50 with themono-helix fiber membrane 52. Pressurized feed water 72 is introducedoutside the mono-helix fiber membrane 52 into the mixed liquor 66. Themixed liquor 66 includes bacteria and protozoa to help breakdown largeorganic waste 74 and develop biological floc to maintain total suspendedsolids (TSS) in the mixed liquor 66.

As shown in FIG. 5A, the pressurized feed water 72 is introduced outsidethe fiber 56 into the mixed liquor 66 and permeate water 64 is drawninto the lumens 62 of the fibers 56. The permeate water 64 can then becarried out one or both ends of the fibers 56. In other embodiments,pressurized air can be used at one end of the fibers 56 to forcepermeate water 64 out of each fiber 56. In some embodiments, the core 54is porous and can collect permeate water 64 from the fibers 56. The feedwater 72 can be introduced near the bottom of the MBR 50. However, thefeed water 72 can alternatively or additionally be introduced near thetop and/or sides of the MBR 50.

Outside the fibers 56, air, oxygen, or other inert gases can be used tosparge the mixed liquor 66 using an aerator 76, as shown in FIGS. 3,5A-5B, and 7A-7B. Dotted arrows 78 in FIGS. 3, 5A, and 7A indicate adirection of flow of small or fine bubbles 80 and large or coarsebubbles 82. The aerator 76 can introduce the fine bubbles 80 into themixed liquor 66 for aeration and circulation. The aerator 76 or aseparate aerator can introduce the coarse bubbles 82 for scouring tohelp reduce fouling on the fibers 56. The MBR 50 can also include an airsparge or back flush cycle to push high pressure air or permeate water64 back through the fibers 56 to help reduce fouling on the fibers 56.The design of the helically-wound fibers 56, in some embodiments, canhelp capture solids and also can help back flush efficiency. Ratherthan, or in addition to the aerator 76, the core 54 can include anaerator to aerate and/or scour the mono helix 60.

FIG. 6 illustrates a dual-helix fiber membrane 84 according to anotherembodiment of the invention. The dual-helix fiber membrane 84 caninclude a first set of fibers 56 and a second set of fibers 86 helicallywound together around a core 54 and secured to headers 58. The layers offibers 56 and 86 can be asymmetrically or symmetrically wound around thecore 54 to create a dual helix 88. The second set of fibers 86 can behydrophobic or hydrophillic, microporous fibers with pores of about 0.1microns in diameter, in some embodiments. The second set of fibers 86can be used to deliver gas, air, or oxygen to scour the dual helix 88and/or aerate the mixed liquor 66 in a localized manner. For example,aeration can be provided by the second set of fibers 86 in very closeproximity to the first set of fibers 56. As shown in FIG. 7A, gas 90 canbe provided to the interior or lumen of the second set of fibers 86 at apressure above local hydrostatic pressure. The gas 90 will then bedelivered out from the pores around the dual helix 88.

The core 54 and the sets of fibers 56, 86 can be constructed and can beoperated similar to the mono-helix fiber membrane 52 described above.For example, in some embodiments, the MBR 50 can include one or moredual-helix fiber membranes 86 coupled together to a permeate watermanifold and submersed in a membrane bioreactor tank. In otherembodiments, the MBR 50 can include a single dual-helix fiber membrane84 in a cylindrical housing, or cartridge 68, with end caps 70, as shownin FIG. 4. The dual helix or helixes 88 can be fixed at both ends toheaders 58 so that the sets of fibers 56, 86 are substantiallystationary or can be fixed at only one end to a single manifold 58 sothat the sets of fibers 56, 86 are moveable (i.e., can sway). In someembodiments, the layers of the dual helix 88 can be regularlyintertwined as follows: fibers 56, fibers 86, fibers 56, fibers 86,etc., where different sizes of the fibers 56, 86 can help define spacingbetween layers. In other embodiments, the layering of the sets of fibers56, 86 in the dual helix 88 can be relatively random.

As shown in FIGS. 7A and 7B, the second set of fibers 86 can allow thegas 90 to be delivered locally along the length of the dual helix 88.The dual helix 88 can increase the effectiveness of scouring, becauseconventional scouring techniques generally only release air from anaerator at one end of the MBR 50. Local aeration with the second set offibers 86 can help prevent the development of dead zones in the MBR 50.In addition, the dual helix 88 can also decrease energy usage, as thepressure only needs to be great enough to diffuse gas out into a small,localized area, rather than up the entire length of the MBR 50. Also,back flushing periods are needed less frequently.

The dual helix 88 can have consistent or varying distributioncharacteristics in both sets of fibers 56, 86, such as patternedporosities, densities, texture, surface structure, cross-sectionalshapes, and/or dimensions (such as lumen size). The varying patternedporosities and densities can allow controllable local environments andimprove bio-reactivity by permitting combined aerobic and anaerobicconditions or various bubble sizes in the second set of fibers 86 in theMBR 50.

The structured designs of the mono helix 60 and the dual helix 88 canoffer controlled spacing between sets of fibers 56 and/or 86. Thevarying density from interior to exterior portions can allow betterfluid-to-fiber contact and more surface area, in comparison toconventional random-packing fiber designs.

As shown in FIG. 7A, pressurized feed water 72 can be introduced outsidethe sets of fibers 56 and 86 into the mixed liquor 66 and permeate water64 can be drawn through the lumen 62 of the first set of fibers 56. Insome embodiments, vacuum can be applied to the lumen 62 to create apressure driving force to drive the permeate water 64 through the lumen62. In some embodiments, a combination of a pressurized feed of fluid tobe treated and a vacuum applied to the lumen 62 can create a pressuredriving force to drive the permeate water 64 through the lumen 62. Thepermeate water 64 can then be carried out one or both ends of the firstset of fibers 56. In some embodiments, the core 54 is porous and cancollect permeate water 64 from the first set of fibers 56. As shown inFIGS. 7A and 7B, the second set of fibers 86 can release air to scourthe dual helix 88 with coarse bubbles 82 and reduce fouling. In someembodiments, the localized scouring of the first set of fibers 56 cantemporarily reduce or substantially stop the permeate flux through thefirst set of fibers 56.

In some embodiments, portions of the dual helix 88 can includebacteria-promoting chemicals and/or the dual helix 88 can includevarying surface energy zones along its length to promote variousbacterial growth patterns. Also, portions of the dual helix 88 caninclude varying fiber chemistries in order to create anaerobic andaerobic zones for particular bacteria.

In some embodiments, one or more types of additional filtration media(not shown) can be wrapped around the core 54 between the sets of fibers56 and/or 86. The additional filtration media can be another set offibers and/or a porous sheet and can be structured to achieve aerationand/or filtration functions for specific applications. The additionalfiltration media can also help define spacing between the layers of thesets of fibers 56 and/or 86 and can act as a support for a biofilm.

In some embodiments, the permeate water 64 collected from the MBR 50 canbe further filtered with another filtering device, such as a reverseosmosis (RO) module (not shown). In some embodiments, the permeate water64 that feeds the RO module can also be recycled through the lumen 62 ofthe first set of fibers 56. Salts and organics from the permeate water64 in the lumen 62 can accumulate to a steady state, and the salts cancreate an osmotic draw of the permeate water 64, lowering the energyrequired to achieve a constant permeate flux. In addition, the organicscan diffuse back into the mixed liquor 66, improving the efficiency ofbiological digestion. The salts can also have a local anti-foulingeffect, acting as a bactericide on the surfaces of the sets of fibers56, 86.

According to some embodiments of the invention, FIG. 8 illustratesradial flow of fluid through the mono-helix fiber membrane 52 or thedual-helix fiber membrane 84. In the radial flow mode, the mono-helixfiber membrane 52 or the dual-helix fiber membrane 84 can be woundaround a core 90, positioned in the cylindrical housing or cartridge 68,and secured with headers or tubesheets 92. Fluid to be treated can bedirected into the interior of the core 90 and can then flow radiallyoutward through the mono-helix fiber membrane 52 or the dual-helix fibermembrane 84. The core 90 can be perforated or otherwise sufficientlyporous to allow fluid to flow through it radially. The fluid can flowradially (as indicated by arrows 94) with respect to a longitudinal axis96 of the mono-helix fiber membrane 52, the dual-helix fiber membrane84, and/or the core 90. The fluid can then flow into a space 98 adjacentto an internal annular wall 100 of the cartridge 68 and then toward oneor more outlets 102. This radial flow of fluid can help reduce the fluidpressure drop across the membrane, while still providing enoughresidence time to achieve filtration. Although shown positioned inside acartridge 68, the mono-helix fiber membrane 52 or the dual-helix fibermembrane 84 can be submerged in a open chamber or tank.

According to some embodiments of the invention, FIG. 9 illustratesparallel flow of fluid through the mono-helix fiber membrane 52 or thedual-helix fiber membrane 84. The mono-helix fiber membrane 52 or thedual-helix fiber membrane 84 can be wound around the core 90, positionedin the cylindrical housing or cartridge 68, and secured with headers ortubesheets 92. An impervious wrap 104 can be wrapped around themono-helix fiber membrane 52 or the dual-helix fiber membrane 84. Theentire mono-helix fiber membrane 52 or dual-helix fiber membrane 84between the tubesheets 92 can be covered with the impervious wrap 104,except for an open portion 106 (e.g., a portion adjacent to one of thetubesheets 92). A seal 108 can be placed between the impervious wrap 104and the internal annular wall 100 of the cartridge 68.

Fluid to be treated can be directed into the interior of the core 90 andcan then flow through one or more passageways 110 to the mono-helixfiber membrane 52 or the dual-helix fiber membrane 84. Due to theimpervious wrap 104 and/or the seal 108, the fluid entering through thepassageways 110 can flow down the length of the mono-helix fibermembrane 52 or the dual-helix fiber membrane 84 until it reaches theopen portion 106, where it can flow toward the outlets 102. The fluidcan flow parallel (as indicated by arrows 112) to the longitudinal axis96 of the mono-helix fiber membrane 52, the dual-helix fiber membrane84, and/or the core 90. The core 90 can include a “dead-end” 114 toensure that all fluid flows through the passageways 110 toward themono-helix fiber membrane 52 or the dual-helix fiber membrane 84.Although shown positioned inside a cartridge 68, the mono-helix fibermembrane 52 or the dual-helix fiber membrane 84 can be submerged in aopen chamber or tank.

During the process of fluid filtration, some or all of the fluidpermeates through the membrane walls of the fibers. As a result, thereis a decrease in volumetric flow of the fluid on the outside of thefibers. In a membrane module with a constant packing fraction for thefibers or a constant cross-sectional area between the fibers, thisdecrease in volumetric flow results in a decrease in the velocity of thefluid. Also, as fluid permeates through the membrane walls, theremaining fluid becomes more concentrated in the particles and speciesrejected by the membrane walls. These two phenomenon of reduced velocityand increased concentration reduce the mass transfer performance of themembrane and a reduction in performance is often observed.

In some embodiments of the invention, the winding parameters of thefibers in the membrane module can be altered in order to increase thepacking fraction of the fibers in the direction of fluid flow (i.e., topack the fibers more tightly). Increasing the packing fraction of thefibers results in decreasing the free space between the outside of thefibers. In other words, the cross-sectional area where fluid flowsbetween the fibers decreases in the direction of fluid flow. In thismanner, some embodiments of the invention can be used to maintain ahigher fluid velocity and high mass transfer efficiency.

The increase in packing fraction and decrease in cross-sectional areabetween the fibers can be used in the radial flow mode of FIG. 8 or thecross flow mode of FIG. 9 in situations where extra flow recirculationis often used to offset the reduction in fluid velocity. In FIG. 8, thepacking fraction can be increased in the direction of the radial flow(as indicated by arrows 94) to maintain fluid flow velocity on theoutside of the fibers. In other words, the fibers can be packed moreloosely adjacent to the core 90 and more tightly as the distance betweenthe fibers and the core 90 increases. More specifically, each layer offibers can be wound using a different packing fraction in order tocompensate for the drop in fluid velocity as the fluid flows radiallyoutward away from the core 90. In FIG. 9, the packing fraction can beincreased in the direction of fluid flow (as indicated by the arrows112). This increase in packing fraction can result in a smaller diameterat one end of the mono or dual helix. Alternatively, this increase inpacking fraction can result in the mono or dual helix being more denseat one end with the same diameter along its longitudinal length.

The increase in packing fraction and decrease in cross-sectional areabetween the fibers can also be used in the radial flow dead-end mode ofFIG. 8 or the parallel flow dead-end mode of FIG. 9 where substantiallyall the fluid permeates through the membrane walls. In FIG. 8, thepacking fraction can be increased in the direction of the radial flow(as indicated by the arrows 94) to maintain fluid flow velocity on theoutside of the fibers. In other words, the fibers can be packed moreloosely adjacent to the core 90 and more tightly as the distance betweenthe fibers and the core 90 increases. More specifically, each layer offibers can be wound using a different packing fraction in order tocompensate for the drop in fluid velocity as the fluid flows radiallyoutward away from the core 90. In FIG. 9, the packing fraction can beincreased in the direction of fluid flow (as indicated by the arrows112). This increase in packing fraction can result in a smaller diameterat one end of the mono or dual helix. Alternatively, this increase inpacking fraction can result in the mono or dual helix being more denseat one end with the same diameter along its longitudinal length.

It will be appreciated by those skilled in the art that while theinvention has been described above in connection with particularembodiments and examples, the invention is not necessarily so limited,and that numerous other embodiments, examples, uses, modifications anddepartures from the embodiments, examples and uses are intended to beencompassed by the claims attached hereto. The entire disclosure of eachpatent and publication cited herein is incorporated by reference, as ifeach such patent or publication were individually incorporated byreference herein. Various features and advantages of the invention areset forth in the following claims.

1. A membrane module comprising: a first plurality of fibers that arehelically wound, the first plurality of fibers capable of filteringfluids; a second plurality of fibers that are helically wound along atleast a portion of a length of the first plurality of fibers in order tocreate a dual helix, the second plurality of fibers having differentproperties than the first plurality of fibers in order to achievedifferent filtering functionalities; and a filtration media wrappedbetween fibers in the dual helix.
 2. The module of claim 1 wherein thefirst plurality of fibers is hydrophilic and the second plurality offibers is hydrophobic.
 3. The module of claim 1 wherein the secondplurality of fibers deliver gas from a source of gas, the gas beingdelivered adjacent to an exterior surface of the first plurality offibers to substantially reduce flow through the first plurality offibers while the first plurality of fibers are being scoured.
 4. Themodule of claim 1 wherein the first plurality of fibers are configuredfor outside-in filtration.
 5. The module of claim 1 and furthercomprising a vacuum pump; and wherein at least one of a pressurized feedof fluid to be treated and a vacuum created by the vacuum pump isapplied to the first plurality of fibers in order to draw permeate waterthrough lumens of the first plurality of fibers.
 6. The module of claim1 wherein gas from a source of gas is selectively provided to lumens ofthe second plurality of fibers at a pressure greater than a localhydrostatic pressure.
 7. The module of claim 1 wherein the firstplurality of fibers are ultrafiltration membranes and the secondplurality of fibers are microporous membranes.
 8. The module of claim 7wherein the first plurality of fibers include pores up to about 0.01microns in diameter and the second plurality of fibers include pores upto about 0.1 microns in diameter.
 9. The module of claim 1 wherein atleast one end of the first plurality of fibers are potted and coupled toa permeate manifold.
 10. The module of claim 1 wherein a plurality ofdual helixes are coupled together to a permeate manifold to create asubmersible module.
 11. The module of claim 1 wherein the dual helix ispositioned inside a cylindrical housing.
 12. The module of claim 1wherein the module is provided with a discharge for permeate water outof lumens of the first plurality of fibers from at least one end of thefirst plurality of fibers.
 13. The module of claim 1 wherein the firstplurality of fibers and the second plurality of fibers are more dense inan interior layer than an exterior layer.
 14. The module of claim 1wherein the first plurality of fibers and the second plurality of fibersinclude along their lengths at least one of varying pore sizes,patterned porosities, varying fiber cross-sectional shapes, varyingfiber textures, and varying fiber dimensions.
 15. The module of claim 14wherein the varying fiber dimensions include varying lumen sizes. 16.The module of claim 1 wherein the first plurality of fibers and thesecond plurality of fibers include varying surface structure along theirlengths.
 17. The module of claim 1 wherein one of the first plurality offibers and the second plurality of fibers has a larger diameter in orderto define spacing between layers.
 18. The module of claim 1 wherein themodule is adapted for use in one of a drinking water purificationsystem, a wastewater treatment system, and an industrial process watertreatment system.
 19. The module of claim 1 wherein fluid to be treatedflows one of radially with respect to a longitudinal axis of the dualhelix and parallel to the longitudinal axis of the dual helix.
 20. Themodule of claim 1 wherein at least one of the first plurality of fibersand the second plurality of fibers provide an open cross-sectional areafor fluid flow that decreases in the direction of fluid flow.
 21. Amembrane module comprising: a first plurality of fibers that arehelically wound, the first plurality of fibers capable of filteringfluids; a second plurality of fibers that are helically wound along atleast a portion of a length of the first plurality of fibers in order tocreate a dual helix, the second plurality of fibers having differentproperties than the first plurality of fibers in order to achievedifferent filtering functionalities; and a core, the first plurality offibers and the second plurality of fibers being helically wound aroundthe core, the core being a porous hollow cylinder, the core including apacked bed of filtration media positioned inside the core.
 22. Themodule of claim 21 wherein the core is used to aerate the dual helix.23. The module of claim 21 wherein the core includes perforations. 24.The module of claim 21 wherein the core is adapted to collect one ofpermeate water and fluid to be treated.
 25. A membrane modulecomprising: a first plurality of fibers that are helically wound, thefirst plurality of fibers capable of filtering fluids; a secondplurality of fibers that are helically wound along at least a portion ofa length of the first plurality of fibers in order to create a dualhelix, the second plurality of fibers having different properties thanthe first plurality of fibers in order to achieve different filteringfunctionalities; and a core, the first plurality of fibers and thesecond plurality of fibers being helically wound around the core, thecore being a porous hollow cylinder, the core including an ultravioletlight source positioned inside of the core.
 26. A membrane modulecomprising: a first plurality of fibers that are helically wound, thefirst plurality of fibers capable of filtering fluids; and a secondplurality of fibers that are helically wound along at least a portion ofa length of the first plurality of fibers in order to create a dualhelix, the second plurality of fibers having different properties thanthe first plurality of fibers in order to achieve different filteringfunctionalities; the dual helix including fibers of varying chemistriesalong its length in order to create anaerobic and aerobic zones.
 27. Amembrane module comprising: a first plurality of fibers that arehelically wound, the first plurality of fibers capable of filteringfluids; and a second plurality of fibers that are helically wound alongat least a portion of a length of the first plurality of fibers in orderto create a dual helix, the second plurality of fibers having differentproperties than the first plurality of fibers in order to achievedifferent filtering functionalities; portions of a length of the firstplurality of fibers and the second plurality of fibers includingbacteria-promoting chemicals.
 28. A membrane module comprising: a firstplurality of fibers that are helically wound, the first plurality offibers capable of filtering fluids; and a second plurality of fibersthat are helically wound along at least a portion of a length of thefirst plurality of fibers in order to create a dual helix, the secondplurality of fibers having different properties than the first pluralityof fibers in order to achieve different filtering functionalities; thefirst plurality of fibers and the second plurality of fibers includingvarying surface energy zones along their lengths to promote variousbacterial growth patterns.
 29. A membrane module for use in a membranebioreactor, the membrane module comprising: a first plurality of fibersthat are helically wound, the first plurality of fibers beinghydrophilic, the first plurality of fibers capable of filteringwastewater; and a second plurality of fibers that are helically woundalong at least a portion of a length of the first plurality of fibers inorder to create a dual helix, the second plurality of fibers beinghydrophobic, the second plurality of fibers capable of selectivelydelivering gas locally with respect to the first plurality of fibers inorder to scour the first plurality of fibers; the dual helix includingfibers of varying chemistries along its length in order to createanaerobic and aerobic zones.
 30. The module of claim 29 wherein thesecond plurality of fibers provide oxygen from a source of oxygen tobacteria in the membrane bioreactor.
 31. The module of claim 29 whereinthe second plurality of fibers deliver gas from a source of gas, the gasbeing delivered adjacent to an exterior surface of the first pluralityof fibers to substantially reduce flow through the first plurality offibers while the first plurality of fibers are being scoured.
 32. Themodule of claim 29 wherein the first plurality of fibers are configuredfor outside-in filtration.
 33. The module of claim 29 wherein gas isselectively provided to lumens of the second plurality of fibers at apressure greater than a local hydrostatic pressure.
 34. The module ofclaim 29 wherein the first plurality of fibers are ultrafiltrationmembranes and the second plurality of fibers are microporous membranes.35. The module of claim 34 wherein the first plurality of fibers includepores up to about 1 micron in diameter and the second plurality offibers include pores up to about 10 microns in diameter.
 36. The moduleof claim 29 wherein at least one end of the first plurality of fibersare potted and coupled to a permeate manifold.
 37. The module of claim29 wherein a plurality of dual helixes are coupled together to apermeate manifold to create a submersible module.
 38. The module ofclaim 29 wherein at least one of the first plurality of fibers and thesecond plurality of fibers provide an open cross-sectional area forfluid flow that decreases in the direction of fluid flow.
 39. A membranemodule for use in a membrane bioreactor, the membrane module comprising:a first plurality of fibers that are helically wound, the firstplurality of fibers being hydrophilic, the first plurality of fiberscapable of filtering wastewater; and a second plurality of fibers thatare helically wound along at least a portion of a length of the firstplurality of fibers in order to create a dual helix, the secondplurality of fibers being hydrophobic, the second plurality of fiberscapable of selectively delivering gas locally with respect to the firstplurality of fibers in order to scour the first plurality of fibers;portions of a length of the first plurality of fibers and the secondplurality of fibers including bacteria-promoting chemicals.
 40. Amembrane module for use in a membrane bioreactor, the membrane modulecomprising: a first plurality of fibers that are helically wound, thefirst plurality of fibers being hydrophilic, the first plurality offibers capable of filtering wastewater; and a second plurality of fibersthat are helically wound along at least a portion of a length of thefirst plurality of fibers in order to create a dual helix, the secondplurality of fibers being hydrophobic, the second plurality of fiberscapable of selectively delivering gas locally with respect to the firstplurality of fibers in order to scour the first plurality of fibers; thefirst plurality of fibers and the second plurality of fibers includingvarying surface energy zones along their lengths to promote variousbacterial growth patterns.